In some examples, an embolization device includes multiple sections with three-dimensional non-helical structures when deployed at a vascular site. The multiple sections include a first section and one or more second sections that are smaller than the first section. The first section may have a deployed structure configured to anchor the device at a vascular site (e.g., a blood vessel) of a patient while each of the one or more second sections may be formed from loops that configured to pack and obstruct the vascular site. In some cases, the embolization device also includes a third section having a deployed configuration with multiple helical windings or loops is configured to anchor the embolization device at the vascular site.